diff --git a/cmd/tsconnect/README.md b/cmd/tsconnect/README.md
index fc01876a3..bb4dddfe6 100644
--- a/cmd/tsconnect/README.md
+++ b/cmd/tsconnect/README.md
@@ -38,3 +38,12 @@ The client is also available as an NPM package. To build it, run:
 ```
 
 That places the output in the `pkg/` directory, which may then be uploaded to a package registry (or installed from the file path directly).
+
+To do two-sided development (on both the NPM package and code that uses it), run:
+
+```
+./tool/go run ./cmd/tsconnect dev-pkg
+
+```
+
+This serves the module at http://localhost:9090/pkg/pkg.js and the generated wasm file at http://localhost:9090/pkg/main.wasm. The two files can be used as drop-in replacements for normal imports of the NPM module.
diff --git a/cmd/tsconnect/build-pkg.go b/cmd/tsconnect/build-pkg.go
index 26700d192..e0220b42f 100644
--- a/cmd/tsconnect/build-pkg.go
+++ b/cmd/tsconnect/build-pkg.go
@@ -11,13 +11,12 @@ import (
 	"os"
 	"path"
 
-	esbuild "github.com/evanw/esbuild/pkg/api"
 	"github.com/tailscale/hujson"
 	"tailscale.com/version"
 )
 
 func runBuildPkg() {
-	buildOptions, err := commonSetup(prodMode)
+	buildOptions, err := commonPkgSetup(prodMode)
 	if err != nil {
 		log.Fatalf("Cannot setup: %v", err)
 	}
@@ -31,10 +30,6 @@ func runBuildPkg() {
 		log.Fatalf("Cannot clean %s: %v", *pkgDir, err)
 	}
 
-	buildOptions.EntryPoints = []string{"src/pkg/pkg.ts", "src/pkg/pkg.css"}
-	buildOptions.Outdir = *pkgDir
-	buildOptions.Format = esbuild.FormatESModule
-	buildOptions.AssetNames = "[name]"
 	buildOptions.Write = true
 	buildOptions.MinifyWhitespace = true
 	buildOptions.MinifyIdentifiers = true
diff --git a/cmd/tsconnect/common.go b/cmd/tsconnect/common.go
index da823829a..bea345902 100644
--- a/cmd/tsconnect/common.go
+++ b/cmd/tsconnect/common.go
@@ -8,6 +8,7 @@ import (
 	"fmt"
 	"io/ioutil"
 	"log"
+	"net"
 	"os"
 	"os/exec"
 	"path"
@@ -68,6 +69,18 @@ func commonSetup(dev bool) (*esbuild.BuildOptions, error) {
 	}, nil
 }
 
+func commonPkgSetup(dev bool) (*esbuild.BuildOptions, error) {
+	buildOptions, err := commonSetup(dev)
+	if err != nil {
+		return nil, err
+	}
+	buildOptions.EntryPoints = []string{"src/pkg/pkg.ts", "src/pkg/pkg.css"}
+	buildOptions.Outdir = *pkgDir
+	buildOptions.Format = esbuild.FormatESModule
+	buildOptions.AssetNames = "[name]"
+	return buildOptions, nil
+}
+
 // cleanDir removes files from dirPath, except the ones specified by
 // preserveFiles.
 func cleanDir(dirPath string, preserveFiles ...string) error {
@@ -90,6 +103,27 @@ func cleanDir(dirPath string, preserveFiles ...string) error {
 	return nil
 }
 
+func runEsbuildServe(buildOptions esbuild.BuildOptions) {
+	host, portStr, err := net.SplitHostPort(*addr)
+	if err != nil {
+		log.Fatalf("Cannot parse addr: %v", err)
+	}
+	port, err := strconv.ParseUint(portStr, 10, 16)
+	if err != nil {
+		log.Fatalf("Cannot parse port: %v", err)
+	}
+	result, err := esbuild.Serve(esbuild.ServeOptions{
+		Port:     uint16(port),
+		Host:     host,
+		Servedir: "./",
+	}, buildOptions)
+	if err != nil {
+		log.Fatalf("Cannot start esbuild server: %v", err)
+	}
+	log.Printf("Listening on http://%s:%d\n", result.Host, result.Port)
+	result.Wait()
+}
+
 func runEsbuild(buildOptions esbuild.BuildOptions) esbuild.BuildResult {
 	log.Printf("Running esbuild...\n")
 	result := esbuild.Build(buildOptions)
diff --git a/cmd/tsconnect/dev-pkg.go b/cmd/tsconnect/dev-pkg.go
new file mode 100644
index 000000000..f66290bf4
--- /dev/null
+++ b/cmd/tsconnect/dev-pkg.go
@@ -0,0 +1,17 @@
+// Copyright (c) 2022 Tailscale Inc & AUTHORS All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+import (
+	"log"
+)
+
+func runDevPkg() {
+	buildOptions, err := commonPkgSetup(devMode)
+	if err != nil {
+		log.Fatalf("Cannot setup: %v", err)
+	}
+	runEsbuildServe(*buildOptions)
+}
diff --git a/cmd/tsconnect/dev.go b/cmd/tsconnect/dev.go
index 4cbe6dfed..c2a264cea 100644
--- a/cmd/tsconnect/dev.go
+++ b/cmd/tsconnect/dev.go
@@ -6,10 +6,6 @@ package main
 
 import (
 	"log"
-	"net"
-	"strconv"
-
-	esbuild "github.com/evanw/esbuild/pkg/api"
 )
 
 func runDev() {
@@ -17,22 +13,5 @@ func runDev() {
 	if err != nil {
 		log.Fatalf("Cannot setup: %v", err)
 	}
-	host, portStr, err := net.SplitHostPort(*addr)
-	if err != nil {
-		log.Fatalf("Cannot parse addr: %v", err)
-	}
-	port, err := strconv.ParseUint(portStr, 10, 16)
-	if err != nil {
-		log.Fatalf("Cannot parse port: %v", err)
-	}
-	result, err := esbuild.Serve(esbuild.ServeOptions{
-		Port:     uint16(port),
-		Host:     host,
-		Servedir: "./",
-	}, *buildOptions)
-	if err != nil {
-		log.Fatalf("Cannot start esbuild server: %v", err)
-	}
-	log.Printf("Listening on http://%s:%d\n", result.Host, result.Port)
-	result.Wait()
+	runEsbuildServe(*buildOptions)
 }
diff --git a/cmd/tsconnect/tsconnect.go b/cmd/tsconnect/tsconnect.go
index 91feaf727..6719e45dd 100644
--- a/cmd/tsconnect/tsconnect.go
+++ b/cmd/tsconnect/tsconnect.go
@@ -36,6 +36,8 @@ func main() {
 	switch flag.Arg(0) {
 	case "dev":
 		runDev()
+	case "dev-pkg":
+		runDevPkg()
 	case "build":
 		runBuild()
 	case "build-pkg":